1. Field of the Invention
Embodiments of the invention relate to the structure and fabrication of a control circuit, and more particularly, to a carbon nanotubes control circuit. Although the embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for a carbon nanotubes control circuit of a pixel in an active matrix light emitting diodes display module.
2. Discussion of the Related Art
Active matrix display panels provide high resolution, good image quality, wide color gamut and fast response time with less power consumption. Thus, the Active Matrix Liquid Crystal Display (AMLCD) dominates both current mobile-sized and large-sized display panel markets. However, since Liquid Crystal Display (LCD) is non-emissive, a back light is required that is consistently on when the display is in working status. Because the back light is consistently on, false off-state pixels can more readily occur. Most importantly, the light from the back light needs to pass through multiple layers that contain thin film transistors (TFTs), LCD, polarizers, and color filters to be visible. These layers can block about 95% of the back light and interfere with readability of a display under the sunlight.
To circumvent these deficiencies, an array of emissive organic light emitting diodes (OLEDs) is used, instead of an LCD with a back light, to make an AMOLED display panel. However, due to the inherent instability of organic materials, the lifetime, brightness and working circumstances of AMOLED display panels are limited. In contrast, light emitting diodes made of inorganic crystalline semiconductors, such as gallium nitrides, are known to have a lifetime greater than 100,000 hours and efficiency of >300 lm/Watts. Furthermore, the physical properties of inorganic crystalline semiconductors can withstand harsh environmental conditions, such as elevated temperatures and high pressures.
LED based displays have been widely reported and patented. For example, U.S. Pat. No. 5,789,766 describes a monolithic and passively addressable LED display with amorphous silicon driver circuits. Several other patents, such as, U.S. Pat. No. 8,058,663 and U.S. Pat. No. 8,642,363, disclose monolithic full-colored active matrix LED (“AMLED”) micro-displays using flip-chip technologies.
Both passive matrix and active matrix LEDs can be implemented with thin film transistors in the control circuits. The fabrication of control circuits for LED pixels is typically implemented with amorphous silicon (a-Si) thin film transistors or poly-crystalline silicon thin film transistors on the emissive side. However, due to the low field effect mobilities of a-Si TFTs and the tolerance of poly-crystalline silicon fabrication, providing sufficient current to drive the LED pixels can be problematic. Furthermore, the fabrication of TFTs on emissive side decreases the aperture ratio.